Salaam.
It is not like not believing in Prophet Muhammed. For, the rule in the Qur’an is that we should not discriminate in favor of or against any of God’s Prophets. (2:136, 2:285)
That means we must accept each and every one of them with equal fervor.
That is what accrues from 2:62 and 5:69 also.
For, Belief in God, Belief in the Hereafter, and Good Deeds are the only things sought by each and every one of God’s Prophets.
Whatever else we find in the Scriptures are only the details.
That means belief in any one of God's Prophets means belief in all His Prophets.
Conversly, rejecting any of God's Prophets amounts to rejecting all of God's Prophets.
Obviously, all those who believe in the basics, accept truth wherever it is found.
The subject you have raised is so important, that it should be made very clear.
The bane of religion is that its leaders have more often than not complicated matters, and confounded things.
Thus they have separated the people from the Right Path, and scattered them away! (6:151-152-153)
Regards,
A. Ismail Sait.